Ceramic matrix composites (CMC) are used for components in high-temperature areas of gas turbines. CMC walls may be formed by laminating multiple layers of ceramic fabric or fibers in a ceramic matrix. However, interlaminar stresses work to damage the interlayer bonds and separate the layers. Alternately, three-dimensionally woven CMC walls offer improved through-thickness properties over 2D laminated walls. 3D walls are reinforced at the preform stage, during which a ceramic fiber structure is woven to nearly final shape by weaving, braiding, or knitting. However, this technique is not feasible for oxide-based CMCs without considerable investment, because infiltrating a particulate loaded ceramic slurry into a thick, tightly packed, brittle fiber preform is extremely difficult. It can result in incomplete and heterogeneous matrix infiltration, even when using state-of-the-art processing, and even for relatively thin 3D preforms such as 3-4 mm. The problem is worse with more realistic component wall thicknesses such as 5 mm or more. U.S. Pat. Nos. 4,568,594, 4,888,311, 4,921,822, 5,077,243, 5,294,387, 5,306,554, and 5,460,637 teach oxide matrix CMCs in which the largest matrix particles are preferred to be greater than 1 micron in diameter. This size is taught as preferable both for sintering shrinkage control and high temperature stability. However, these large particle sizes are especially difficult to infiltrate into a thick, densely packed fibrous preform, because the preform acts as a filter. All of the above patents also teach bimodal particle size distributions including a smaller size range much less than 1 micron. The smaller particles infiltrate nicely, but they are segregated from the larger particles via the filtration effect.
In addition, 3D preforms have the following constraints:                Limited to simple shapes such as extruded, flat, or cylindrical, depending on production method        Not conducive to localized optimization of reinforcement geometry        High development costs for complex shapes, due to custom loom setups, etc.        3D preforms often cannot be compacted for maximum fiber volume without losing the through-thickness reinforcement benefit        Long development time & expense precludes iterative design approaches        Expertise resides in a limited number of specialty shops, none of which offer all available options.        